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* pahole and parsing data: --count
       [not found]                   ` <0eae329c-d448-4d04-c240-0850a93278a5-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
@ 2020-07-01 11:25                     ` Arnaldo Carvalho de Melo
       [not found]                       ` <20200701112534.GQ29008-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
  0 siblings, 1 reply; 3+ messages in thread
From: Arnaldo Carvalho de Melo @ 2020-07-01 11:25 UTC (permalink / raw)
  To: dwarves-u79uwXL29TY76Z2rM5mHXA; +Cc: Joe Lawrence

Hi,

	I've been implementing pretty printing in pahole:

[acme@quaco pahole]$ git log --oneline v1.17..
5631fdcea1bb (HEAD -> master, acme.korg/pretty, acme.korg/master) pahole: Introduce --count, just like dd's
272bc75024b4 man-pages: Add information about stdin raw data pretty printing
66835f9e190c pahole: Add support for base type arrays
1a67d6e70090 pahole: Factor out base_type__fprintf_value()
6fb98aa1209f pahole: Support char arrays when dumping from stdin
a231d00f8d08 pahole: Print comma at the end of field name + field value
1b2cdda38c0a dwarves: Introduce tag__is_array()
a83313fb2252 pahole: Pretty print base types in structs from stdin
cc65946e3068 dwarves: Adopt tag__is_base_type() from ctrace.c
d8079c6d373a pahole: Hex dump a type from stdio when it isn't a tty
38109ab45fe0 spec: Fix date
[acme@quaco pahole]$

	The latest changeset shows what this is about, see its example
below, please help testing and suggesting whatever needs you have
regarding pretty printing.

	Now to implement --skip.

Regards,

- Arnaldo

From 5631fdcea1bbe2bcb8c673ff0bb0fdc9fdc2875d Mon Sep 17 00:00:00 2001
From: Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Date: Wed, 1 Jul 2020 08:14:58 -0300
Subject: [PATCH] pahole: Introduce --count, just like dd's

  $ objcopy -O binary --only-section=.altinstructions ~/git/build/v5.7-rc2+/vmlinux .altinstructions
  $ pahole --count 2 alt_instr  < .altinstructions
  {
  	.instr_offset = 0xffffffffffe0e690,
  	.repl_offset = 0x4873,
  	.cpuid = 0x70,
  	.instrlen = 0x5,
  	.replacementlen = 0x5,
  	.padlen = 0,
  },
  {
  	.instr_offset = 0xffffffffffe0e683,
  	.repl_offset = 0x486b,
  	.cpuid = 0x129,
  	.instrlen = 0x5,
  	.replacementlen = 0x5,
  	.padlen = 0,
  },
  $

Signed-off-by: Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 dwarves.h          |  2 ++
 man-pages/pahole.1 |  8 +++++++-
 pahole.c           | 13 +++++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/dwarves.h b/dwarves.h
index 0170f251bcd4..f224d05b28c3 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -54,6 +54,7 @@ struct conf_load {
 
 /** struct conf_fprintf - hints to the __fprintf routines
  *
+ * @count - Just like 'dd', stop pretty printing input after 'count' records
  * @flat_arrays - a->foo[10][2] becomes a->foo[20]
  * @classes_as_structs - class f becomes struct f, CTF doesn't have a "class"
  * @cachelinep - pointer to current cacheline, so that when expanding types we keep track of it,
@@ -68,6 +69,7 @@ struct conf_fprintf {
 	int32_t	   type_spacing;
 	int32_t	   name_spacing;
 	uint32_t   base_offset;
+	uint32_t   count;
 	uint32_t   *cachelinep;
 	uint8_t	   indent;
 	uint8_t	   expand_types:1;
diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index 26c14cb6fd2c..7e8207756432 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -60,6 +60,8 @@ See the EXAMPLES section for more usage suggestions.
 It also pretty prints whatever is fed to its standard input, according to the
 type specified, see the EXAMPLE session.
 
+Use --count to state how many records should be pretty printed.
+
 .SH OPTIONS
 pahole supports the following options.
 
@@ -72,6 +74,10 @@ or file URLs (e.g.: file://class_list.txt)
 .B \-c, \-\-cacheline_size=SIZE
 Set cacheline size to SIZE bytes.
 
+.TP
+.B \-\-count=COUNT
+Pretty print the first COUNT records from input.
+
 .TP
 .B \-E, \-\-expand_types
 Expand class members. Useful to find in what member of inner structs where an
@@ -482,7 +488,7 @@ $
 $ ls -la versions
 -rw-rw-r--. 1 acme acme 7616 Jun 25 11:33 versions
 $
-$ pahole -C modversion_info drivers/scsi/sg.ko < versions | head -12
+$ pahole --count 3 -C modversion_info drivers/scsi/sg.ko < versions
 {
       .crc = 0x8dabd84,
       .name = "module_layout",
diff --git a/pahole.c b/pahole.c
index 03909525bf15..1b84f5c2fa4a 100644
--- a/pahole.c
+++ b/pahole.c
@@ -802,6 +802,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_suppress_packed	   308
 #define ARGP_just_unions	   309
 #define ARGP_just_structs	   310
+#define ARGP_count		   311
 
 static const struct argp_option pahole__options[] = {
 	{
@@ -822,6 +823,12 @@ static const struct argp_option pahole__options[] = {
 		.arg  = "CLASS_NAME",
 		.doc  = "Show just this class"
 	},
+	{
+		.name = "count",
+		.key  = ARGP_count,
+		.arg  = "COUNT",
+		.doc  = "Print only COUNT input records"
+	},
 	{
 		.name = "find_pointers_to",
 		.key  = 'f',
@@ -1145,6 +1152,8 @@ static error_t pahole__options_parser(int key, char *arg,
 		just_unions = true;			break;
 	case ARGP_just_structs:
 		just_structs = true;			break;
+	case ARGP_count:
+		conf.count = atoi(arg);			break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}
@@ -1315,6 +1324,7 @@ static int tag__stdio_fprintf_value(struct tag *type, struct cu *cu, FILE *fp)
 {
 	int _sizeof = tag__size(type, cu), printed = 0;
 	void *instance = malloc(_sizeof);
+	uint32_t count = 0;
 
 	if (instance == NULL)
 		return -ENOMEM;
@@ -1322,6 +1332,9 @@ static int tag__stdio_fprintf_value(struct tag *type, struct cu *cu, FILE *fp)
 	while (fread(instance, _sizeof, 1, stdin) == 1) {
 		printed += tag__fprintf_value(type, cu, instance, _sizeof, fp);
 		printed += fprintf(fp, ",\n");
+
+		if (conf.count && ++count == conf.count)
+			break;
 	}
 
 	return printed;
-- 
2.21.3

^ permalink raw reply	[flat|nested] 3+ messages in thread

* pahole and parsing data: --skip
       [not found]                       ` <20200701112534.GQ29008-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
@ 2020-07-01 11:44                         ` Arnaldo Carvalho de Melo
       [not found]                           ` <20200701114421.GR29008-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
  0 siblings, 1 reply; 3+ messages in thread
From: Arnaldo Carvalho de Melo @ 2020-07-01 11:44 UTC (permalink / raw)
  To: dwarves-u79uwXL29TY76Z2rM5mHXA; +Cc: Joe Lawrence, Jiri Olsa, Namhyung Kim

Em Wed, Jul 01, 2020 at 08:25:34AM -0300, Arnaldo Carvalho de Melo escreveu:
> 	The latest changeset shows what this is about, see its example
> below, please help testing and suggesting whatever needs you have
> regarding pretty printing.
> 
> 	Now to implement --skip.

Now to implement --seek, this time in bytes, so that we can, for
instance, pretty print perf.data records, looking at 'perf report -D'
and getting the offset of the start of a series of 'struct
perf_event_attr' or 'struct perf_event_header'.

- Arnaldo

commit 44af7c02b5d0a7f2b93fab9fda45907cd6fe0827
Author: Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Date:   Wed Jul 1 08:36:28 2020 -0300

    pahole: Implement --skip, just like dd
    
      $ objcopy -O binary --only-section=__versions drivers/scsi/sg.ko versions
      $ pahole -C modversion_info drivers/scsi/sg.ko
      struct modversion_info {
            long unsigned int          crc;                  /*     0     8 */
            char                       name[56];             /*     8    56 */
    
            /* size: 64, cachelines: 1, members: 2 */
      };
      $ pahole --count 3 -C modversion_info drivers/scsi/sg.ko < versions
      {
            .crc = 0x8dabd84,
            .name = "module_layout",
      },
      {
            .crc = 0x45e4617b,
            .name = "no_llseek",
      },
      {
            .crc = 0xa23fae8c,
            .name = "param_ops_int",
      },
      $ pahole --skip 1 --count 2 -C modversion_info drivers/scsi/sg.ko < versions
      {
            .crc = 0x45e4617b,
            .name = "no_llseek",
      },
      {
            .crc = 0xa23fae8c,
            .name = "param_ops_int",
      },
      $
    
    Signed-off-by: Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

diff --git a/dwarves.h b/dwarves.h
index f224d05b28c3..24f9c7c37843 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -55,6 +55,7 @@ struct conf_load {
 /** struct conf_fprintf - hints to the __fprintf routines
  *
  * @count - Just like 'dd', stop pretty printing input after 'count' records
+ * @skip - Just like 'dd', skip 'count' records when pretty printing input
  * @flat_arrays - a->foo[10][2] becomes a->foo[20]
  * @classes_as_structs - class f becomes struct f, CTF doesn't have a "class"
  * @cachelinep - pointer to current cacheline, so that when expanding types we keep track of it,
@@ -71,6 +72,7 @@ struct conf_fprintf {
 	uint32_t   base_offset;
 	uint32_t   count;
 	uint32_t   *cachelinep;
+	uint32_t   skip;
 	uint8_t	   indent;
 	uint8_t	   expand_types:1;
 	uint8_t	   expand_pointers:1;
diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index 7e8207756432..db820cca323f 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -78,6 +78,10 @@ Set cacheline size to SIZE bytes.
 .B \-\-count=COUNT
 Pretty print the first COUNT records from input.
 
+.TP
+.B \-\-skip=COUNT
+Skip COUNT input records.
+
 .TP
 .B \-E, \-\-expand_types
 Expand class members. Useful to find in what member of inner structs where an
@@ -502,6 +506,16 @@ $ pahole --count 3 -C modversion_info drivers/scsi/sg.ko < versions
       .name = "param_ops_int",
 },
 $
+$ pahole --skip 1 --count 2 -C modversion_info drivers/scsi/sg.ko < versions
+{
+      .crc = 0x45e4617b,
+      .name = "no_llseek",
+},
+{
+      .crc = 0xa23fae8c,
+      .name = "param_ops_int",
+},
+$
 .fi
 .P
 
diff --git a/pahole.c b/pahole.c
index 1b84f5c2fa4a..7d8431c64423 100644
--- a/pahole.c
+++ b/pahole.c
@@ -803,6 +803,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_just_unions	   309
 #define ARGP_just_structs	   310
 #define ARGP_count		   311
+#define ARGP_skip		   312
 
 static const struct argp_option pahole__options[] = {
 	{
@@ -829,6 +830,12 @@ static const struct argp_option pahole__options[] = {
 		.arg  = "COUNT",
 		.doc  = "Print only COUNT input records"
 	},
+	{
+		.name = "skip",
+		.key  = ARGP_skip,
+		.arg  = "COUNT",
+		.doc  = "Skip COUNT input records"
+	},
 	{
 		.name = "find_pointers_to",
 		.key  = 'f',
@@ -1154,6 +1161,8 @@ static error_t pahole__options_parser(int key, char *arg,
 		just_structs = true;			break;
 	case ARGP_count:
 		conf.count = atoi(arg);			break;
+	case ARGP_skip:
+		conf.skip = atoi(arg);			break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}
@@ -1325,11 +1334,17 @@ static int tag__stdio_fprintf_value(struct tag *type, struct cu *cu, FILE *fp)
 	int _sizeof = tag__size(type, cu), printed = 0;
 	void *instance = malloc(_sizeof);
 	uint32_t count = 0;
+	uint32_t skip = conf.skip;
 
 	if (instance == NULL)
 		return -ENOMEM;
 
 	while (fread(instance, _sizeof, 1, stdin) == 1) {
+		if (skip) {
+			--skip;
+			continue;
+		}
+
 		printed += tag__fprintf_value(type, cu, instance, _sizeof, fp);
 		printed += fprintf(fp, ",\n");
 

^ permalink raw reply	[flat|nested] 3+ messages in thread

* pahole and parsing data: --seek_bytes, dissecting perf.data files
       [not found]                           ` <20200701114421.GR29008-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
@ 2020-07-01 12:46                             ` Arnaldo Carvalho de Melo
  0 siblings, 0 replies; 3+ messages in thread
From: Arnaldo Carvalho de Melo @ 2020-07-01 12:46 UTC (permalink / raw)
  To: dwarves-u79uwXL29TY76Z2rM5mHXA
  Cc: Joe Lawrence, Jiri Olsa, Namhyung Kim, Andrii Nakryiko, Song Liu

Em Wed, Jul 01, 2020 at 08:44:21AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Wed, Jul 01, 2020 at 08:25:34AM -0300, Arnaldo Carvalho de Melo escreveu:
> > 	The latest changeset shows what this is about, see its example
> > below, please help testing and suggesting whatever needs you have
> > regarding pretty printing.
> > 
> > 	Now to implement --skip.

> Now to implement --seek, this time in bytes, so that we can, for
> instance, pretty print perf.data records, looking at 'perf report -D'
> and getting the offset of the start of a series of 'struct
> perf_event_attr' or 'struct perf_event_header'.

Here it is with more complex examples dissecting perf.data file data
structures, including BPF related structs:

commit fe284221448c950d2ba17bce91d19c484d6580a0
Author: Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Date:   Wed Jul 1 09:17:38 2020 -0300

    pahole: Introduce --seek_bytes
    
    Works with stdio, will work with files where we'll use plain lseek and
    allow for pretty printing trailer structs.
    
    E.g.:
    
      $ objcopy -O binary --only-section=__versions drivers/scsi/sg.ko versions
      $ pahole -C modversion_info drivers/scsi/sg.ko
      struct modversion_info {
              long unsigned int          crc;                  /*     0     8 */
              char                       name[56];             /*     8    56 */
    
              /* size: 64, cachelines: 1, members: 2 */
      };
      $ pahole --count 2 -C modversion_info drivers/scsi/sg.ko < versions
      {
            .crc = 0x8dabd84,
            .name = "module_layout",
      },
      {
            .crc = 0x45e4617b,
            .name = "no_llseek",
      },
      $ pahole --skip 1 --count 1 -C modversion_info drivers/scsi/sg.ko < versions
      {
            .crc = 0x45e4617b,
            .name = "no_llseek",
      },
    
    Then the equivalent, skipping sizeof(modversion_info) explicitely:
    
      $ pahole --seek_bytes 64 --count 1 -C modversion_info drivers/scsi/sg.ko < versions
      {
            .crc = 0x45e4617b,
            .name = "no_llseek",
      },
      $
    
    Using a perf.data file generated by 'perf record':
    
      $ perf report -D | head -18
      # To display the perf.data header info, please use --header/--header-only options.
      #
    
      0x130 [0x20]: event: 79
      .
      . ... raw event: size 32 bytes
      .  0000:  4f 00 00 00 00 00 20 00 1f 00 00 00 00 00 00 00  O..... .........
      .  0010:  31 30 9b 3c 00 00 00 00 2e 53 f8 0c 52 8c 01 00  10.<.....S�.R...
    
      0 0x130 [0x20]: PERF_RECORD_TIME_CONV: unhandled!
    
      0x150 [0x28]: event: 73
      .
      . ... raw event: size 40 bytes
      .  0000:  49 00 00 00 00 00 28 00 01 00 00 00 00 00 00 00  I.....(.........
      .  0010:  50 7e 00 00 00 00 00 00 00 00 00 00 00 00 00 00  P~..............
      .  0020:  00 00 00 00 00 00 00 00                          ........
    
      $ pahole --seek_bytes 0x130 --count 1 -C perf_event_header < perf.data
      {
            .type = 0x4f,
            .misc = 0,
            .size = 0x20,
      },
      $ printf "0x%x\n" 79
      0x4f
      $ pahole --seek_bytes 0x150 --count 1 -C perf_event_header < perf.data
      {
            .type = 0x49,
            .misc = 0,
            .size = 0x28,
      },
      $ printf "0x%x\n" 73
      0x49
      $
    
    Now to use more complex types, again using perf.data files.
    
      # perf record -a sleep 1
      [ perf record: Woken up 1 times to write data ]
      [ perf record: Captured and wrote 3.834 MB perf.data (31853 samples) ]
      # perf report -D | grep -m1 -B20 PERF_RECORD_BPF
      0x6aa0 [0x58]: event: 17
      .
      . ... raw event: size 88 bytes
      .  0020:  5f 37 62 65 34 39 65 33 39 33 34 61 31 32 35 62  _7be49e3934a125b
      .  0030:  61 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  a...............
      .  0040:  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
      .  0050:  00 00 00 00 00 00 00 00                          ........
    
      0 0 0x6aa0 [0x58]: PERF_RECORD_KSYMBOL addr ffffffffc03e0e90 len 203 type 1 flags 0x0 name bpf_prog_7be49e3934a125ba
    
      0x6af8 [0x38]: event: 18
      .
      . ... raw event: size 56 bytes
      .  0000:  12 00 00 00 00 00 38 00 01 00 00 00 11 00 00 00  ......8.........
      .  0020:  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
      .  0030:  00 00 00 00 00 00 00 00                          ........
    
      0 0 0x6af8 [0x38]: PERF_RECORD_BPF_EVENT type 1, flags 0, id 17
      Binary file (standard input) matches
      # pahole -C perf_record_bpf_event ~/bin/perf
      struct perf_record_bpf_event {
            struct perf_event_header   header;               /*     0     8 */
            __u16                      type;                 /*     8     2 */
            __u16                      flags;                /*    10     2 */
            __u32                      id;                   /*    12     4 */
            __u8                       tag[8];               /*    16     8 */
    
            /* size: 24, cachelines: 1, members: 5 */
            /* last cacheline: 24 bytes */
      };
      # pahole -C perf_record_bpf_event --seek_bytes 0x6af8 --count 1 ~/bin/perf < perf.data
      {
            .header = 0x12 0x00 0x00 0x00 0x00 0x00 0x38 0x00,
            .type = 0x1,
            .flags = 0,
            .id = 0x11,
            .tag = { 0, 0, 0, 0, 0, 0, 0, 0},
      },
      # printf "0x%x\n" 18
      0x12
      # pahole -C perf_record_ksymbol ~/bin/perf
      struct perf_record_ksymbol {
            struct perf_event_header   header;               /*     0     8 */
            __u64                      addr;                 /*     8     8 */
            __u32                      len;                  /*    16     4 */
            __u16                      ksym_type;            /*    20     2 */
            __u16                      flags;                /*    22     2 */
            char                       name[256];            /*    24   256 */
    
            /* size: 280, cachelines: 5, members: 6 */
            /* last cacheline: 24 bytes */
      };
      # pahole -C perf_record_ksymbol --seek_bytes 0x6aa0 --count 1 ~/bin/perf < perf.data
      {
            .header = 0x11 0x00 0x00 0x00 0x00 0x00 0x58 0x00,
            .addr = 0xffffffffc03e0e90,
            .len = 0xcb,
            .ksym_type = 0x1,
            .flags = 0,
            .name = "bpf_prog_7be49e3934a125ba",
      },
      # printf "0x%x\n" 17
      0x11
      #
    
    Need to recursively pretty print substructs, but all seems to work with
    the simple hexdump.
    
    Signed-off-by: Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

diff --git a/dwarves.h b/dwarves.h
index 24f9c7c37843..1b118d03ec15 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -13,6 +13,7 @@
 #include <obstack.h>
 #include <dwarf.h>
 #include <elfutils/libdwfl.h>
+#include <sys/types.h>
 
 #include "dutil.h"
 #include "list.h"
@@ -56,6 +57,7 @@ struct conf_load {
  *
  * @count - Just like 'dd', stop pretty printing input after 'count' records
  * @skip - Just like 'dd', skip 'count' records when pretty printing input
+ * @seek_bytes - Number of bytes to seek, if stdin only from start, when we have --pretty FILE, then from the end as well with negative numbers
  * @flat_arrays - a->foo[10][2] becomes a->foo[20]
  * @classes_as_structs - class f becomes struct f, CTF doesn't have a "class"
  * @cachelinep - pointer to current cacheline, so that when expanding types we keep track of it,
@@ -72,6 +74,7 @@ struct conf_fprintf {
 	uint32_t   base_offset;
 	uint32_t   count;
 	uint32_t   *cachelinep;
+	off_t	   seek_bytes;
 	uint32_t   skip;
 	uint8_t	   indent;
 	uint8_t	   expand_types:1;
diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index db820cca323f..ad4e92d716cf 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -516,6 +516,14 @@ $ pahole --skip 1 --count 2 -C modversion_info drivers/scsi/sg.ko < versions
       .name = "param_ops_int",
 },
 $
+This is equivalent to:
+
+$ pahole --seek_bytes 64 --count 1 -C modversion_info drivers/scsi/sg.ko < versions
+{
+	.crc = 0x45e4617b,
+	.name = "no_llseek",
+},
+$
 .fi
 .P
 
diff --git a/pahole.c b/pahole.c
index 7d8431c64423..245a3f2f14f7 100644
--- a/pahole.c
+++ b/pahole.c
@@ -3,7 +3,7 @@
 
   Copyright (C) 2006 Mandriva Conectiva S.A.
   Copyright (C) 2006 Arnaldo Carvalho de Melo <acme-4qZELD6FgxhWk0Htik3J/w@public.gmane.org>
-  Copyright (C) 2007-2008 Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
+  Copyright (C) 2007- Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
 */
 
 #include <argp.h>
@@ -804,6 +804,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_just_structs	   310
 #define ARGP_count		   311
 #define ARGP_skip		   312
+#define ARGP_seek_bytes		   313
 
 static const struct argp_option pahole__options[] = {
 	{
@@ -836,6 +837,12 @@ static const struct argp_option pahole__options[] = {
 		.arg  = "COUNT",
 		.doc  = "Skip COUNT input records"
 	},
+	{
+		.name = "seek_bytes",
+		.key  = ARGP_seek_bytes,
+		.arg  = "BYTES",
+		.doc  = "Seek COUNT input records"
+	},
 	{
 		.name = "find_pointers_to",
 		.key  = 'f',
@@ -1163,6 +1170,8 @@ static error_t pahole__options_parser(int key, char *arg,
 		conf.count = atoi(arg);			break;
 	case ARGP_skip:
 		conf.skip = atoi(arg);			break;
+	case ARGP_seek_bytes:
+		conf.seek_bytes = strtol(arg, NULL, 0);	break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}
@@ -1329,6 +1338,25 @@ static int tag__fprintf_value(struct tag *type, struct cu *cu, void *instance, i
 	return tag__fprintf_hexdump_value(type, cu, instance, _sizeof, fp);
 }
 
+static int pipe_seek(FILE *fp, off_t offset)
+{
+	char bf[4096];
+	int chunk = sizeof(bf);
+
+	if (chunk > offset)
+		chunk = offset;
+
+	while (fread(bf, chunk, 1, stdin) == 1) {
+		offset -= chunk;
+		if (offset == 0)
+			return 0;
+		if (chunk > offset)
+			chunk = offset;
+	}
+
+	return offset == 0 ? 0 : -1;
+}
+
 static int tag__stdio_fprintf_value(struct tag *type, struct cu *cu, FILE *fp)
 {
 	int _sizeof = tag__size(type, cu), printed = 0;
@@ -1339,6 +1367,12 @@ static int tag__stdio_fprintf_value(struct tag *type, struct cu *cu, FILE *fp)
 	if (instance == NULL)
 		return -ENOMEM;
 
+	if (conf.seek_bytes && pipe_seek(stdin, conf.seek_bytes) < 0) {
+		int err = --errno;
+		fprintf(stderr, "Couldn't --seek_bytes %ld\n", conf.seek_bytes);
+		return err;
+	}
+
 	while (fread(instance, _sizeof, 1, stdin) == 1) {
 		if (skip) {
 			--skip;

^ permalink raw reply	[flat|nested] 3+ messages in thread

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     [not found]   ` <20200624173038.GC20203@kernel.org>
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2020-07-01 11:25                     ` pahole and parsing data: --count Arnaldo Carvalho de Melo
     [not found]                       ` <20200701112534.GQ29008-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2020-07-01 11:44                         ` pahole and parsing data: --skip Arnaldo Carvalho de Melo
     [not found]                           ` <20200701114421.GR29008-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2020-07-01 12:46                             ` pahole and parsing data: --seek_bytes, dissecting perf.data files Arnaldo Carvalho de Melo

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